Clément, the only son of a mother who has been divorced for almost as long as his age, is a smart but also very curious nine-year-old boy. When he's not at school, never losing his camera, he tirelessly crisscrosses the old streets of his small town. In this small neighborhood where everyone knows each other, his favorite pastime is to observe the different grown-ups, photographing them on the spot when he is with them. Sometimes in secret to try to understand the way adults live and behave, and through these meetings to discover the secrets of adulthood and the secrets of happiness. He does not want to grow up but he is very much in love with his friend Astrid, a reciprocal feeling and the two live a deep tenderness for each other, to the point of having already promised each other for each other. As Christmas approaches, Clement's curiosity will drag him into a dirty police affair because of a murder. Then a second murder happens, then a third...